The stethoscope is placed near the antecubital artery as well as no audio will be hear when there is adequate stress to shut off the artery. When the pressure is gradually launched, the noise of blood jetting through the vessel by the vibrations of the wall surface is called the Korotkoff appears. Please note that the audio is usually overestimated due to the fact that audio can still be heard also after depreciation of the cuff.
This info was composed in the Textbook of Medical Physiology by Guyton and Hall.
** Disclaimer: we are not medical experts.